Effect of Disulfide Cyclization of Ultrashort Cationic Lipopeptides on Antimicrobial Activity and Cytotoxicity

Total Biosynthesis of Circular Bacteriocins by Merging the Genetic Engineering and Enzymatic Catalysis

Circular bacteriocins are known for their structural stability and effective antimicrobial properties, positioning them as potential natural food preservatives. However, their widespread application is impeded by restricted availability. This research developed a total biosynthesis platform for circular bacteriocins, with a focus on AS-48 by involving recombinant production of the linear precursor in Escherichia coli, followed by enzymatic cyclization of the precursor into cyclic AS-48 using the ligase butelase-1 in vitro. An important discovery is that, aside from fusion tags, the C-terminal motif LE and LEKKK also could affect the expression yield of the precursor. This biosynthesis platform is both versatile and high-yielding, achieving yields of 10-20 mg/L of AS-48. Importantly, the biosynthetic AS-48 exhibited a secondary structure and antimicrobial activities comparable to those of the native molecules. As such, this work proposes an effective synthetic approach for circular bacteriocins, facilitating their advancement and application in the food industry.

Two promising Bacillus-derived antifungal lipopeptide leads AF4 and AF5 and their combined effect with fluconazole on the in vitro Candida glabrata biofilms

Introduction: Candida species are endowed with the ability to produce biofilms, which is one of the causes of pathogenicity, as biofilms protect yeasts from antifungal drugs. Candida glabrata (Nakaseomyces glabrata) is one of the most prevalent pathogenic yeasts in humans and a biofilm producer. Methods: The study was aimed at evaluating the combined effects of two highly promising antifungal biomolecules (AF4 and AF5) lipopeptide in nature, chromatographically purified to homogeneity from Bacillus subtilis (B. subtilis) and the standard antifungal fluconazole (at different concentrations) to demonstrate C. glabrata biofilm formation inhibition. Biofilm production and inhibition were evaluated by quantification of the biofilm biomass and metabolic activity using crystal violet (CV) staining and XTT reduction assays, respectively. Microscopic techniques such as confocal scanning laser microscopy (CSLM) and scanning electron microscopy (SEM) were employed to visualize biofilm formation and inhibition. Results and Discussion: Compared to untreated and fluconazole-treated biofilms, an enhanced in vitro anti-biofilm effect of the antifungal lipopeptides AF4/AF5 alone and their combinations with fluconazole was established. The lipopeptides AF4/AF5 alone at 8 and 16 μg/mL exhibited significant biomass and metabolic activity reductions. SEM and CSLM images provided evidence that the lipopeptide exposure results in architectural alterations and a significant reduction of C. glabrata biofilms, whereas (2', 7'-dichlorofluorescin diacetate (DCFDA) and propidium iodide (PI) analyses showed reactive oxygen species (ROS) generation along with membrane permeabilization. The estimation of exopolysaccharides (EPS) in AF4/AF5-treated biofilms indicated EPS reduction. The combinations of fluconazole (64/128 μg/mL) and AF4/AF5 lipopeptide (16 μg/mL) were found to significantly disrupt the mature (24 h) biofilms as revealed by CSLM and SEM studies. The CSLM images of biofilms were validated using COMSTAT. The FTIR-analyses indicate the antibiofilm effects of both lipopeptides on 24 h biofilms to support CSLM and SEM observations. The combinations of fluconazole (64/128 μg/mL) and AF4/AF5 lipopeptide were found to disrupt the mature biofilms; the study also showed that the lipopeptides alone have the potentials to combat C. glabrata biofilms. Taken together, it may be suggested that these lipopeptide leads can be optimized to potentially apply on various surfaces to either reduce or nearly eradicate yeast biofilms.

The Study of Antistaphylococcal Potential of Omiganan and Retro-Omiganan Under Flow Conditions

Staphylococcus aureus is considered one of the leading pathogens responsible for infections in humans and animals. The heterogeneous nature of diseases caused by these bacteria is due to the occurrence of multiple strains, differentiated by several mechanisms of antibiotic resistance and virulence factors. One of these is the ability to form biofilm. Biofilm-associated bacteria exhibit a different phenotype that protects them from external factors such as the activity of immune system or antimicrobial substances. Moreover, it has been shown that the majority of persistent and recurrent infections are associated with the presence of the biofilm. Omiganan, an analog of indolicidin - antimicrobial peptide (AMP) derived from bovine neutrophil granules, was found to exhibit high antistaphylococcal and antibiofilm potential. Furthermore, its analog with a reversed sequence (retro-omiganan) was found to display enhanced activity against a variety of pathogens. Based on experience of our group, we found out that counterion exchange can improve the antistaphylococcal activity of AMPs. The aim of this study was to investigate the activity of both compounds against S. aureus biofilm under flow conditions. The advantage of this approach was that it offered the opportunity to form and characterize the biofilm under more controlled conditions. To do this, unique flow cells made of polydimethylsiloxane (PDMS) were developed. The activity against pre-formed biofilm as well as AMPs-treated bacteria was measured. Also, the incorporation of omiganan and retro-omiganan into the channels was conducted to learn whether or not it would inhibit the development of biofilm. The results of the microbiological tests ultimately confirmed the high potential of the omiganan and its retro-analog as well as the importance of counterion exchange in terms of antimicrobial examination. We found out that retro-omiganan trifluoroacetate had the highest biofilm inhibitory properties, however, acetates of both compounds exhibited the highest activity against planktonic and biofilm cultures. Moreover, the developed methodology of investigation under flow conditions allows the implementation of the studies under flow conditions to other compounds.

Quaternary Ammonium Salts of Cationic Lipopeptides with Lysine Residues - Synthesis, Antimicrobial, Hemolytic and Cytotoxic Activities

Ultrashort cationic lipopeptides (USCLs) and quaternary ammonium salts constitute two groups of cationic surfactants with high antimicrobial activity. This study aimed to investigate the influence of quaternization of the amino group of the lysine side chain in USCLs on their antimicrobial, hemolytic and cytotoxic activities. To do this, two series of lipopeptides were synthesized, USLCs and their quaternized analogues containing trimethylated lysine residues - qUSCLs (quaternized ultrashort cationic lipopeptides). Quaternization was performed on a resin during a standard solid-phase peptide synthesis with CH3I as the methylating agent. According to our knowledge, this is the first study presenting on-resin peptide quaternization. The lipopeptides were tested for their antibacterial and antifungal activities against the ESKAPE group (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa and Klebsiella aerogenes) bacteria and Candida glabrata yeast-like fungus. Most of the compounds proved to be active antimicrobial agents with enhanced activity against Gram-positive strains and fungi and a lower against Gram-negative species. In addition, the antimicrobial activity of lipopeptides was increasing with an increase in hydrophobicity but qUSCLs exhibited usually a poorer antimicrobial activity than their parent molecules. Furthermore, the toxicity against red blood cells and human keratinocytes was assessed. It's worth emphasizing that qUSCLs were less toxic than the parent molecules of comparative hydrophobicity. The results of the study proved that qUSCLs can offer a higher selectivity to pathogens over human cells than that of USCLs. Last but not least, quaternization of the peptides could increase their solubility and therefore their bioavailability and utility.

Creation of New Antimicrobial Peptides

Antimicrobial peptides (AMPs) are natural compounds that exhibit potent antimicrobial activity against various microorganisms, including bacteria, fungi, and viruses [...].

Lipidation of Naturally Occurring α-Helical Antimicrobial Peptides as a Promising Strategy for Drug Design

In this paper, we describe the chemical synthesis, preliminary evaluation of antimicrobial properties and mechanisms of action of a novel group of lipidated derivatives of three naturally occurring α-helical antimicrobial peptides, LL-I (VNWKKVLGKIIKVAK-NH₂), LK6 (IKKILSKILLKKL-NH₂), ATRA-1 (KRFKKFFKKLK-NH₂). The obtained results showed that biological properties of the final compounds were defined both by the length of the fatty acid and by the structural and physico-chemical properties of the initial peptide. We consider C₈-C₁₂ length of the hydrocarbon chain as the optimal for antimicrobial activity improvement. However, the most active analogues exerted relatively high cytotoxicity toward keratinocytes, with the exception of the ATRA-1 derivatives, which had a higher selectivity for microbial cells. The ATRA-1 derivatives had relatively low cytotoxicity against healthy human keratinocytes but high cytotoxicity against human breast cancer cells. Taking into account that ATRA-1 analogues carry the highest positive net charge, it can be assumed that this feature contributes to cell selectivity. As expected, the studied lipopeptides showed a strong tendency to self-assembly into fibrils and/or elongated and spherical micelles, with the least cytotoxic ATRA-1 derivatives forming apparently smaller assemblies. The results of the study also confirmed that the bacterial cell membrane is the target for the studied compounds.

Glycosylated Lipopeptides-Synthesis and Evaluation of Antimicrobial Activity and Cytotoxicity

Ultrashort cationic lipopeptides (USCLs) are promising antimicrobial agents that may be used to combat pathogens such as bacteria and fungi. USCLs consist of a few basic amino acid residues and at least one lipid moiety, usually a fatty acid chain. Generally, USCLs are potent antimicrobials but their major shortcoming is a relatively high cytotoxicity and hemolytic activity. Glycopeptide antibiotics (e.g. vancomycin) are essential in combating bacterial infections and are popular in medicinal practice. However, literature concerning the effect of glycosylation of peptides on their antimicrobial activity is rather scarce. For the first time, this study highlights the effect of USCLs glycosylation on in vitro biological activity. The aim of this study was to evaluate the impact of glycosylation of a series of USCLs on antimicrobial activity, cytotoxicity and hemolytic activity. Straight-chain fatty acids (C14, C16, C18) were attached to the N-terminal amino group of tripeptides-SRR-NH₂, RSR-NH₂ and RRS-NH₂. Two groups of the lipopeptides were synthetized, the first with unmodified L-serine (USCLs) and the other with L-serine O-glycosylated by N-acetyl-β-d-glucosamine to produce new class of glycosylated ultrashort cationic lipopeptide (gUSCLs). Both USCLs and gUSCLs were tested against planktonic and biofilm cultures of ESKAPE strains (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, Enterobacter spp.) and Candida glabrata, and hemolytic activity on human erythrocytes and cytotoxicity against the HaCaT cell line was examined. Generally, USCLs and gUSCLs proved to be active against all the tested strains. The highest activity displayed was by lipopeptides containing the C18 fatty acid. Antimicrobial, hemolytic and cytotoxic activities were mainly correlated with amino acid sequence (position of serine/glycosylated serine) and hydrophobicity of molecule and were found to be highly strain-dependent. In general, glycosylation did not guarantee an increased antimicrobial activity or a decreased hemolytic and cytotoxic activities. However, in some cases, gUSCLs proved to be superior to their USCLs analogs. The most pronounced differences were found for peptides with C18 fatty acid and serine at the first and second position against both planktonic cells and biofilm of C. glabrata, as well as the second and third position against S. aureus. It is noteworthy that gUSCLs were also more active against biofilm than were USCLs.

Incorporation of Non-Canonical Amino Acids into Antimicrobial Peptides: Advances, Challenges, and Perspectives

The emergence of antimicrobial resistance is a global health concern and calls for the development of novel antibiotic agents. Antimicrobial peptides seem to be promising candidates due to their diverse sources, mechanisms of action, and physicochemical characteristics, as well as the relatively low emergence of resistance. The incorporation of noncanonical amino acids into antimicrobial peptides could effectively improve their physicochemical and pharmacological diversity. Recently, various antimicrobial peptides variants with improved or novel properties have been produced by the incorporation of single and multiple distinct noncanonical amino acids. In this review, we summarize strategies for the incorporation of noncanonical amino acids into antimicrobial peptides, as well as their features and suitabilities. Recent applications of noncanonical amino acid incorporation into antimicrobial peptides are also presented. Finally, we discuss the related challenges and prospects.

Activity of Novel Ultrashort Cyclic Lipopeptides against Biofilm of Candida albicans Isolated from VVC in the Ex Vivo Animal Vaginal Model and BioFlux Biofilm Model-A Pilot Study

In recent years, clinicians and doctors have become increasingly interested in fungal infections, including those affecting the mucous membranes. Vulvovaginal candidiasis (VVC) is no exception. The etiology of this infection remains unexplained to this day, as well as the role and significance of asymptomatic vaginal Candida colonization. There are also indications that in the case of VVC, standard methods of determining drug susceptibility to antifungal drugs may not have a real impact on their clinical effectiveness-which would explain, among other things, treatment failures and relapse rates. The aim of the study was to verify the promising results obtained previously in vitro using standard methods, in a newly developed ex vivo model, using tissue fragments of the mouse vagina. The main goal of the study was to determine whether the selected ultrashort cyclic lipopeptides (USCLs) and their combinations with fluconazole at specific concentrations are equally effective against Candida forming a biofilm directly on the surface of the vaginal epithelium. In addition, the verification was also performed with the use of another model for the study of microorganisms (biofilms) in vitro-the BioFlux system, under microfluidic conditions. The obtained results indicate the ineffectiveness of the tested substances ex vivo at concentrations eradicating biofilm in vitro. Nevertheless, the relatively most favorable and promising results were still obtained in the case of combination therapy-a combination of low concentrations of lipopeptides (mainly linear analogs) with mycostatic fluconazole. Additionally, using BioFlux, it was not possible to confirm the previously obtained results. However, an inhibiting effect of the tested lipopeptides on the development of biofilm under microfluidic conditions was demonstrated. There is an incompatibility between the classic in vitro methods, the newer BioFlux method of biofilm testing, offering many advantages postulated elsewhere, and the ex vivo method. This incompatibility is another argument for the need, on the one hand, to intensify research on the pathomechanism of VVC, and, on the other hand, to verify and maybe modify the standard methods used in the determination of Candida susceptibility.

Engineering Approaches for the Development of Antimicrobial Peptide-Based Antibiotics

Antimicrobial peptides (AMPs) have received increasing attention as potential alternatives for future antibiotics because of the rise of multidrug-resistant (MDR) bacteria. AMPs are small cationic peptides with broad-spectrum antibiotic activities and different action mechanisms to those of traditional antibiotics. Despite the desirable advantages of developing peptide-based antimicrobial agents, the clinical applications of AMPs are still limited because of their enzymatic degradation, toxicity, and selectivity. In this review, structural modifications, such as amino acid substitution, stapling, cyclization of peptides, and hybrid AMPs with conventional antibiotics or other peptides, will be presented. Additionally, nanodelivery systems using metals or lipids to deliver AMPs will be discussed based on the structural properties and action mechanisms of AMPs.

Silver Nanoparticles as Chlorhexidine and Metronidazole Drug Delivery Platforms: Their Potential Use in Treating Periodontitis

Purpose

Materials and Methods

Results

Conclusion

Antifungal Activity of Linear and Disulfide-Cyclized Ultrashort Cationic Lipopeptides Alone and in Combination with Fluconazole against Vulvovaginal Candida spp

Vulvovaginal candidiasis (VVC) occurs in over 75% of women at least once during their lifetime and is an infection that significantly affects their health. Candida strains resistant to standard azole antifungal therapy and relapses of VVC are more and more common. Hypothetically, biofilm is one of the main reasons of relapses and failure of the therapy. Ultrashort cationic lipopeptides (USCLs) exhibit high antimicrobial activities. Our previous study on USCLs revealed that disulfide cyclization can result in selective antifungal compounds. Therefore, four USCL were selected and their antifungal activity were studied on 62 clinical strains isolated from VVC. The results confirmed previous premises that cyclic analogs have increased selectivity between fungal cells and keratinocytes and improved anticandidal activity compared to their linear analogs against both planktonic and biofilm cultures. On the other hand, linear lipopeptides in combination with fluconazole showed a synergistic effect. It was found that the minimum inhibitory concentrations of the tested compounds in combination with fluconazole were at least four times lower than when used separately. Our results indicate that combination therapy of VVC with USCLs and fluconazole at low non-toxic concentrations can be beneficial owing to the synergistic effect. However, further in vivo studies are needed to confirm this hypothesis.

Gemini Lipopeptide Bearing an Ultrashort Peptide for Enhanced Transfection Efficiency and Cancer-Cell-Specific Cytotoxicity

Cationic gemini lipopeptides are a relatively new class of amphiphilic compounds to be used for gene delivery. Through the possibility of incorporating short peptides with cell-penetrating functionalities, these lipopeptides may be advantageous over traditional cationic lipids. Herein, we report the design, synthesis, and application of a novel cationic gemini lipopeptide for gene delivery. An ultrashort peptide, containing four amino acids, arginine-cysteine-cysteine-arginine, serves as a cationic head group, and two α-tocopherol moieties act as hydrophobic anchoring groups. The new lipopeptide (ATTA) is incorporated into the conventional liposomes, containing 1,2-dioleoyl-3-trimethylammonium-propane (DOTAP) and 1,2-dioleoyl-sn-glycerol-3-phosphoethanolamine (DOPE), at different molar ratios. The formulated liposomes are characterized and screened for better transfection efficiency. Transfection activity in multiple human cell lines from cancerous and noncancerous origins indicates that the inclusion of an optimal ratio of ATTA in the liposomes substantially enhances the transfection efficiency, superior to that of a traditional liposome, DOTAP-DOPE. Cytotoxicity of ATTA-containing formulations against multiple cell lines indicates potentially distinct activity between cancer and noncancer cell lines. Furthermore, lipoplexes of the ATTA-containing formulations with anticancer therapeutic gene, plasmid encoding tumor necrosis factor-related apoptosis-inducing ligand (pTRAIL), induce obviously more cytotoxicity than conventional formulations. The results indicate that arginine-rich cationic lipopeptide appears to be a promising ingredient in gene delivery vector formulations to enhance transfection efficiency and cell-selective cytotoxicity.

Bacterial-Specific Aggregation and Killing of Immunomodulatory Host Defense Peptides

This study involves the design and development of disulfide bridge-linked antimicrobial peptides using the host defense protein Angiogenin 4 (chAng4) as a template. The mini peptides derived from chAng4 (mCA4s) were evaluated for their antibacterial efficacies in various pathogenic bacterial strains, and the role of the oxidation state of thiols in the peptide sequence and its implication on antibacterial properties were explored. A remarkable property of these synthetic mCA4 peptides is their capability to flocculate bacteria and mediate bacterial-specific killing, in the absence of any other external stimulus. mCA4s were further evaluated for their cellular uptake, hemolytic activities, toxicities, and immunomodulatory activities in different eukaryotic cell lines. The results indicate that disulfide bridge-containing cationic amphipathic peptides show superior antibacterial efficacies, are nontoxic and nonhemolytic, and mediate bacterial flocculation and killing, in the absence of external stimuli.

Biological and Physico-Chemical Characteristics of Arginine-Rich Peptide Gemini Surfactants with Lysine and Cystine Spacers

Ultrashort cationic lipopeptides (USCLs) and gemini cationic surfactants are classes of potent antimicrobials. Our recent study has shown that the branching and shortening of the fatty acids chains with the simultaneous addition of a hydrophobic N-terminal amino acid in USCLs result in compounds with enhanced selectivity. Here, this approach was introduced into arginine-rich gemini cationic surfactants. l-cystine diamide and l-lysine amide linkers were used as spacers. Antimicrobial activity against planktonic and biofilm cultures of ESKAPE (Enterococcus faecium, Staphylococcus aureus, Klebsiella pneumoniae, Acinetobacter baumannii, Pseudomonas aeruginosa, and Enterobacter spp.) strains and Candida sp. as well as hemolytic and cytotoxic activities were examined. Moreover, antimicrobial activity in the presence of human serum and the ability to form micelles were evaluated. Membrane permeabilization study, serum stability assay, and molecular dynamics were performed. Generally, critical aggregation concentration was linearly correlated with hydrophobicity. Gemini surfactants were more active than the parent USCLs, and they turned out to be selective antimicrobial agents with relatively low hemolytic and cytotoxic activities. Geminis with the l-cystine diamide spacer seem to be less cytotoxic than their l-lysine amide counterparts, but they exhibited lower antibiofilm and antimicrobial activities in serum. In some cases, geminis with branched fatty acid chains and N-terminal hydrophobic amino acid resides exhibited enhanced selectivity to pathogens over human cells.